gui: Set up libgui_mocks

Move the existing mocks for IGraphicBufferProducer and
IGraphicBufferConsumer over to libs/gui/..., and create a new static
library "libgui_mocks" to hold the mocks.

libsurfaceflinger_unittest is also adjusted as needed to use the new
library.

Test: atest libsurfaceflinger_unittest
Change-Id: I740ae9d999812896f525f86a30c6800f86ed8ca9
diff --git a/services/surfaceflinger/tests/unittests/Android.bp b/services/surfaceflinger/tests/unittests/Android.bp
index 8d98af6..754c5a7 100644
--- a/services/surfaceflinger/tests/unittests/Android.bp
+++ b/services/surfaceflinger/tests/unittests/Android.bp
@@ -55,8 +55,6 @@
         "mock/DisplayHardware/MockComposer.cpp",
         "mock/DisplayHardware/MockDisplay.cpp",
         "mock/DisplayHardware/MockPowerAdvisor.cpp",
-        "mock/gui/MockGraphicBufferConsumer.cpp",
-        "mock/gui/MockGraphicBufferProducer.cpp",
         "mock/MockDispSync.cpp",
         "mock/MockEventControlThread.cpp",
         "mock/MockEventThread.cpp",
@@ -71,6 +69,7 @@
         "libgmock",
         "libcompositionengine",
         "libcompositionengine_mocks",
+        "libgui_mocks",
         "libperfetto_client_experimental",
         "librenderengine_mocks",
         "libtimestats",